import pygame
from pygame.sprite import Sprite

class Alien(Sprite):
    def __init__(self,ai_settings,screen):
        super().__init__()
        self.screen=screen
        self.ai_settings=ai_settings

        self.image=pygame.image.load("images/alien.bmp")
        self.rect=self.image.get_rect()

        self.rect.x=self.rect.width
        self.rect.y=self.rect.height

        self.x=float(self.rect.x)

    def blitme(self):
        self.screen.blit(self.image,self.rect)

    def check_edges(self):
        #如果外星人位于屏幕边缘，就返回True
        screen_rect=self.screen.get_rect()
        if self.rect.right >= screen_rect.right:
            return True
        elif self.rect.left <= 0:
            return True

    def update(self):
        #向左或向右移动外星人
        self.x += (self.ai_settings.alien_speed_factor * self.ai_settings.fleet_direction)
        self.rect.x=self.x


